The National Institutes of Health (NIH), Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), is the lead Federal agency for the conduct of basic and clinical research to develop new contraceptives and to evaluate existing methods of contraception and reproductive health. The Center for Population Research (CPR), within NICHD, was established in 1968 by the Secretary of Health Education and Welfare, with the important goal of developing new contraceptives through the use of contracts and grants. Within CPR, the Contraception and Reproductive Health Branch (CRHB) has long supported several preclinical contraceptive testing facilities as well as facilities for synthetic chemical and synthetic peptide formulation. To further expand their contraceptive development capabilities, in 1996 CRHB established the NICHD Contraceptive Clinical Trials Network (CCTN). The current CCTN has conducted Phase I, II, and III clinical trials of both female and male contraceptive methods. With the recompetition of the CCTN, clinical sites will perform Phase I, II, III, and Phase IV clinical trials of a wide variety of new or existing female contraceptive methods. The proposed study will evaluate contraceptive efficacy , pharmacokinetics, bleeding patterns and safety and side effects of a Nestorone & estradiol ring for women.